1. Field of the Invention
This invention relates to an image heating apparatus like a heating and fixing device mounted on an image forming apparatus such as a copier or a printer and a heat generating rotary member for use in this apparatus, and more particularly to an image heating apparatus of the induction heating type and a heat generating rotary member for use in this apparatus.
2. Related Background Art
A heating apparatus of the induction heating type causes a magnetic field to act on a magnetic metallic member (an electromagnetic induction heat generating member, an induction magnetic material or a magnetic field absorbing electrically conducting material), and effects the heating of a material to be heated by the heat generation by an induced current (a high frequency induced current or an eddy current) produced in the magnetic metallic member, and is effective, for example, as an image heating and fixing apparatus for heating a recording material on which an unfixed toner image is formed and borne and fixing the unfixed toner image as a permanent secured image in an image forming apparatus of the electrophotographic type, the electrostatic recording type, the magnetic recording type or the like.
As an example of the fixing apparatus of the induction heating type, there is disclosed in Japanese Patent Application Laid-Open No. 9-127810 an induction heating and fixing apparatus of the heat roller type for introducing a sheet on which an unfixed toner image is formed into the pressure contact nip portion between an induction-heated fixing roller and a pressure roller and causing the sheet to be nipped and conveyed therebetween, and heating and fixing the unfixed toner image on the sheet by the heat of the fixing roller, characterized by a construction in which the fixing roller is comprised of a hollow metallic roller having good heat conductivity and a non-magnetic characteristic, and a magnetic metallic thin layer of a magnetic metal formed on the outer periphery of the hollow metallic roller, and an induction coil for inducing an induction current in the magnetic metallic thin layer for heating is disposed in the hollow metallic roller.
In this induction heating and fixing apparatus, the fixing roller is constructed with the magnetic metallic thin layer which is a heat generating member being formed on the outer periphery of the non-magnetic hollow metallic roller having good heat conductivity and therefore, by the hollow metallic roller formed of a non-magnetic metal hardly generating heat and functioning as a mandrel and the lowered heat capacity of the heat generating member, it becomes possible to secure mechanical strength sufficiently, and yet achieve rapid temperature rise and the shortening of the pre-heating time.
However, the magnetic flux coupled to the magnetic metallic layer becomes reduced by the non-magnetic metallic layer between the coil and the magnetic metallic layer, and heat generating efficiency could not be said to be sufficiently high.
The present invention has been made in view of the above-noted problem and an object thereof is to provide an image heating apparatus excellent in heat generating efficiency and a heat generating rotary member used in this apparatus.
Another object of the present invention is to provide an image heating apparatus which can suppress the temperature rise of a non-sheet passage portion and a heat generating rotary member used in this apparatus.
Still another object of the present invention is to provide an image heating apparatus comprising:
a heating member; and
an excitation coil for generating a magnetic field to induce an eddy current in the heating member;
the heating member having a magnetic metallic layer and a non-magnetic metallic layer, the coil being disposed on the magnetic metallic layer side of the heating member.
Yet still another object of the present invention is to provide a heat generating rotary member having:
a magnetic metallic layer; and
a non-magnetic metallic layer provided on the outer side of the magnetic metallic layer.
Further objects of the present invention will become apparent from the following detailed description when read with reference to the accompanying drawings.